Question
What is reciprocal mixing?
Answer Options
- A) Two out-of-band signals mixing to generate an in-band spurious signal
- B) In-phase signals cancelling in a mixer resulting in loss of receiver sensitivity
- C) Two digital signals combining from alternate time slots
- D) Local oscillator phase noise mixing with adjacent strong signals to create interference to desired signals
Correct Answer: D
Explanation
Reciprocal mixing is a form of receiver degradation that limits the ability to hear weak signals when a very strong signal is present on a nearby frequency. Unlike simple blocking or intermodulation, reciprocal mixing is specifically caused by imperfections in the receiver’s local oscillator (LO).
Reciprocal mixing occurs when the local oscillator phase noise mixes with adjacent strong signals to create interference to the desired signals. The noise sidebands of the LO, though very weak, mix with the strong adjacent signal and produce mixing products that fall directly into the receiver’s narrow passband, essentially acting as noise that masks the desired weak signal.
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